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The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio , relative risk measures the association between the exposure and the outcome.
If the risk of an adverse event is increased by the exposure rather than decreased, the term relative risk increase (RRI) is used, and it is computed as () /. [ 1 ] [ 2 ] If the direction of risk change is not assumed, the term relative effect is used, and it is computed in the same way as relative risk increase.
The relative risk reduction is 0.5 (50%), while the absolute risk reduction is 0.0001 (0.01%). The absolute risk reduction reflects the low probability of getting colon cancer in the first place, while reporting only relative risk reduction, would run into risk of readers exaggerating the effectiveness of the drug. [5]
Multiple synonyms of AF e are in use: attributable fraction, [1] [3] relative attributable risk, [1] attributable proportion among the exposed, [1] and attributable risk among the exposed. [4] Similarly, attributable risk percent (ARP) is used as a synonym for the attributable risk percent among the exposed. [3]
The case control study can, however, calculate the exposure-odds ratio, which, mathematically, is supposed to approach the relative risk as prevalence falls. Sander Greenland showed that if the prevalence is 10% or less, the disease can be considered rare enough to allow the rare disease assumption. [ 2 ]
The relative risk (RR), also called risk ratio, is simply the risk (probability) of an event relative to some independent variable. This measure of effect size differs from the odds ratio in that it compares probabilities instead of odds , but asymptotically approaches the latter for small probabilities.
The Arrow–Pratt measure of relative risk aversion (RRA) or coefficient of relative risk aversion is defined as [11] = = ″ ′ (). Unlike ARA whose units are in $ −1, RRA is a dimensionless quantity, which allows it to be applied universally.
Theoretically, the total risk in the presence of multiple risk factors can be estimated by multiplying with each relative risk, but is generally much less accurate than using likelihood ratios, and is usually done only because it is much easier to perform when only relative risks are given, compared to, for example, converting the source data ...